docs: def __get_aws_metric(table_name, lookback_window_start, lookback_period,
                       metric_name):
      """ Returns a  metric list from the AWS CloudWatch service, may return
      None if no metric exists
  
      :type table_name: str
      :param table_name: Name of the DynamoDB table
      :type lookback_window_start: int
      :param lookback_window_start: How many minutes to look at
      :type lookback_period: int
      :type lookback_period: Length of the lookback period in minutes
      :type metric_name: str
      :param metric_name: Name of the metric to retrieve from CloudWatch
      :returns: list -- A list of time series data for the given metric, may
      be None if there was no data
      """
      try:
          now = datetime.utcnow()
          start_time = now - timedelta(minutes=lookback_window_start)
          end_time = now - timedelta(
              minutes=lookback_window_start - lookback_period)
  
          return cloudwatch_connection.get_metric_statistics(
              period=lookback_period * 60,
              start_time=start_time,
              end_time=end_time,
              metric_name=metric_name,
              namespace='AWS/DynamoDB',
              statistics=['Sum'],
              dimensions={'TableName': table_name},
              unit='Count')
      except BotoServerError as error:
          logger.error(
              'Unknown boto error. Status: "{0}". '
              'Reason: "{1}". Message: {2}'.format(
                  error.status,
                  error.reason,
                  error.message))
          raise